1. Field of the Invention
The present invention relates to an ink-jet recording apparatus which ejects ink from a recording device to a recording medium and records thereon.
2. Description of the Related Art
Hitherto, recording apparatuses serving as printers, copying machines, and facsimile machines or those used as output apparatuses such as integrated-type electronic apparatuses and workstations including computers, word processors, and the like have been formed in which images including characters and the like are recorded on recording media such as paper sheets and plastic films in accordance with image data including character data. The recording apparatuses are categorized into ink-jet types, wire-dot types, thermal types, laser-beam types, and the like. An ink-jet-type recording apparatus (hereinafter referred to as an ink-jet recording apparatus) records on a recording medium by ejecting ink thereto from a recording device (recording head) and has a characteristic superior to the other types in that high precision can be easily obtained, a high-speed and quiet operation can be performed, and it can be manufactured at a low cost. Various color ink-jet recording apparatuses have been developed in response to increasing requirements for color recording apparatuses. In order to increase the recording speed, the ink-jet apparatus generally includes a recording head formed with a plurality of integrated recording devices in which a plurality of integrated ink-nozzles and liquid paths are used for ejecting ink, and includes a plurality of the recording heads for a plurality of colors.
FIGS. 1 shows a printer in which the recording head prints a recording sheet. Ink cartridges 101 are shown in the drawing. Each ink cartridge 101 includes an ink tank containing black, cyan, magenta, or yellow ink, and a recording head 102. FIG. 2 shows a plurality of ink nozzles 201, viewed in the Z-direction, disposed on each recording head 102. In FIG. 1, a sheet-transfer roller 103 and an assist roller 104 rotate in directions of arrows shown in the drawing so as to transfer a sheet P in the Y-direction by holding the same. Sheet-feeding rollers 105 feed recording sheets while holding the sheet P in the same manner as the rollers 103 and 104. A carriage 106 supports four ink cartridges 101 and moves the same while printing. The carriage 106 waits in a home position h shown by a dotted line in the drawing when printing is not performed or the recording heads are restored.
The carriage 106 disposed at the home position h before printing starts to move in the X-direction in response to a printing command, and performs printing by ejecting ink through a plurality of the ink nozzles 201 disposed on the recording heads 102. The carriage 106 is restored to the home position when printing of data is completed at the other end of the recording sheet and starts again printing in the X-direction.
A method, for recording in a black-and-white mode at a speed higher than that in a color mode by using the same recording head which has the same number of ink nozzles having the same distance therebetween and using the same black and other colors described above, is disclosed in, for example, Japanese Patent No. 2652405. In the method, a high speed recording is possible without increasing the driving frequency of the recording heads by performing recording in a primary scanning direction (the X-direction) alternately in black with a recording head ejecting black ink and in black with recording heads ejecting other color inks of which a mixture forms a black colored ink.
However, smaller ink droplets must be ejected and the density of recording pixels must be increased in order to reduce jagged edges and dots of black characters and the like and to increase levels of gradation of black color for outputting more photograph-like color images of higher quality.
A method to meet with these requirements is considered in that the amount of ink ejection is reduced by using recording heads having the same number of ink nozzles and the same nozzle density of 300 dpi or 600 dpi as of known recording heads. However, in this method, the recording speed is reduced compared with a known method because the number of movements in a primary scanning direction must be increased so as to fill in gaps in a secondary scanning direction.
Another method is considered in that the amount of ink ejection is reduced by using recording heads having an increased number of ink nozzles so as to have the same width of recording line as that of the known recording heads and an increased nozzle density of 1200 dpi. Although in this method, the recording speed is not reduced, manufacturing costs are increased significantly because the number of ink nozzles is increased by twice of four times that of the known recording heads.
Accordingly, it is an object of the present invention to provide an ink-jet recording apparatus in which high-resolution images can be recorded without reducing the recording speed for black images.
To this end, according to an aspect of the present invention, an ink-jet recording apparatus for performing recording by ejecting ink onto a recording medium while moving a recording head relative to the recording medium in a scanning direction comprises a first nozzle unit including a plurality of nozzles for ejecting black ink disposed in line in a direction different from the scanning direction; and a second nozzle unit including a plurality of nozzles for ejecting colored inks disposed in line in a direction different from the scanning direction and at a density higher than a density of the nozzles included in the first nozzle unit, the plurality of nozzles for ejecting colored inks being capable of forming black ink by mixing colored inks. The first nozzle unit records a black image and the second nozzle unit records with a mixture of colored inks ejected by the second nozzle unit in a region of the black image in which recording is not performed by the first nozzle unit, whereby the black image is recorded with a resolution higher than a resolution of the black image when recorded only by the first nozzle unit.
According to another aspect of the present invention, an ink-jet recording apparatus for performing recording by ejecting ink onto a recording medium while moving a recording head relative to the recording medium in a scanning direction comprises a first nozzle unit including a plurality of nozzles for ejecting black ink disposed in line in a direction different from the scanning direction; and a second nozzle unit including a plurality of nozzles for ejecting colored inks disposed in line in a direction different from the scanning direction and at a density higher than a density of the nozzles included in the first nozzle unit, the plurality of nozzles for ejecting colored inks being capable of forming black ink by mixing colored inks. Recording is selectively performed in one of a first recording mode in which a black image is recorded by the first nozzle unit and a second recording mode in which the first nozzle unit records the black image and the second nozzle unit records with a mixture of colored inks ejected by the second nozzle unit, in a region of the black image in which recording is not performed by the first nozzle unit, whereby the black image is recorded with a resolution higher than a resolution of the black image when recorded only by the first nozzle unit.
According to still another aspect of the present invention, an ink-jet recording apparatus for performing recording by ejecting ink onto a recording medium while moving a recording head relative to the recording medium in a scanning direction comprises a first nozzle unit including a plurality of nozzles for ejecting black ink disposed in line in a direction different from the scanning direction; and a second nozzle unit including a plurality of nozzles for ejecting colored inks disposed in line in a direction different from the scanning direction and at a density higher than a density of the nozzles included in the first nozzle unit, the plurality of nozzles for ejecting colored inks being capable of forming black ink by mixing colored inks. A region of a black image capable of being recorded by the first nozzle unit is recorded with black ink ejected by the first nozzle unit and with a mixture of colored inks ejected by the second nozzle unit, and a remaining region of the black image which is not recorded by the first nozzle unit is recorded with the mixture of colored inks ejected by the second nozzle unit, whereby the black image is recorded with a resolution higher than a resolution of the black image when recorded only by the first nozzle unit.
According to yet another aspect of the present invention, an ink-jet recording apparatus for performing recording by ejecting ink onto a recording medium while moving a recording head relative to the recording medium in a scanning direction comprises a first nozzle unit including a plurality of nozzles for ejecting black ink disposed in line in a direction different from the scanning direction; and a second nozzle unit including a plurality of nozzles for ejecting colored inks disposed in line in a direction different from the scanning direction and at a density higher than a density of the nozzles included in the first nozzle unit, the plurality of nozzles for ejecting colored inks being capable of forming black ink by mixing colored inks. Recording is selectively performed in one of a first recording mode in which a black image is recorded only by the first nozzle unit and a second recording mode in which a region of the black image capable of being recorded by the first nozzle unit is recorded with black ink ejected by the first nozzle unit and with a mixture of colored inks ejected by the second nozzle unit, and a remaining region of the black image which is not recorded by the first nozzle unit is recorded with the mixture of colored inks ejected by the second nozzle unit, whereby the black image is recorded with a resolution higher than a resolution of the black image when recorded only by the first nozzle unit.
According to a further aspect of the present invention, an ink-jet recording method for performing recording by ejecting ink onto a recording medium while moving a recording head relative to the recording medium in a scanning direction comprises the steps of providing a first nozzle unit including a plurality of nozzles for ejecting black ink disposed in line in a direction different from the scanning direction, and a second nozzle unit including a plurality of nozzles for ejecting colored inks disposed in line in a direction different from the scanning direction and at a density higher than a density of the nozzles included in the first nozzle unit, the plurality of nozzles for ejecting colored inks being capable of forming black ink by mixing colored inks; and recording a black image by the first nozzle unit and recording in a region of the black image in which recording is not performed by the first nozzle unit by the second nozzle unit with a mixture of colored inks ejected by the second nozzle unit, whereby the black image is recorded with a resolution higher than a resolution of the black image when recorded only by the first nozzle unit.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.